1. Field of the Invention
The present invention relates to apparatus and methods for testing fiber optics, specifically, fiber-optic testing apparatus for testing fiber-optic harnesses and related methods.
2. Description of Related Art
Due to its flexibility and ability to be bundled, fiber optic systems have become an extremely effective telecommunication and networking medium for transmitting both analog and digital data signals. For example, as a result of the substantial difference in the amount of attenuation of the signal in the fiber vs. signal attenuation in electrical conductors and cables, fiber optic systems have been employed to replace copper wiring used to provide long-distance communications. Also, fiber optic systems can provide a higher bandwidth, i.e., the light signals can be modulated at rates as high as 40 Gb/s or more, and through wavelength division multiplexing, each fiber in a fiber-optic bundle can support numerous independent channels.
Fiber optic systems are also employed to provide short distance communications. In a building or a vehicle, for example, application of fiber optics instead of electrical conductors can not only save space due to its higher bandwidth capability, but can enhance signal quality, i.e., fiber optics are not affected by electromagnetic interference. Fiber optics also have the advantage of being able to be employed in areas where flammable fumes are present, without the danger of ignition inherent with electrical transmission media.
Such characteristics were recognized by the U.S. Air Force as early as 1976 when it began replacing electrical wiring harnesses in certain aircraft with optical datalinks in an effort to reduce weight and to provide radiofrequency interference, electromagnetic interference, and electromagnetic pulse immunity. The optical datalinks were installed and routed through the aircraft in harnesses similar to that used for electrical wires.
There are two methods used to test these optical datalink harnesses. The first, and traditionally most accurate method, is testing one channel at a time with probes that are referenced and mated with the channel under test. Such methodology is described, for example, in U.S. Pat. No. 5,940,559 by Noll, titled “Fiber-optic Test Probe and Connector Adapter for Testing Fiber-optic Connector Harnesses,” and in U.S. Pat. No. 7,060,966 by Taylor et al., titled “Fiber Optic Tester.” The second method is to use a fiber optic harness tester, such as, for example, a multi-channel tester manufactured by DIT-MCO, having offices in Kansas City, Mo., to test multiple channels. The fiber-optic harness tester comprises multiple fiber-optic mating harnesses (optical test leads) adapted to connect to each harness connector in the aircraft. The mating harnesses of the tester include connectors having fiber optic termini, which mate with fiber optic termini in matched connectors of the aircraft harnesses. The mating harnesses also include connectors that are plugged into fiber optic light ports in a central testing unit which includes a controller computer that cycles between all the fiber-optic channels and records measurements. An analyzer converts electrical signals to light signals and transmits the light signals over the optical fiber of the fiber-optic mating harness, and through the aircraft harness being tested, which is returned through another set of optical fibers of another fiber-optic mating harness. The analyzer then converts the received-light signals to an electrical signal used to measure attenuation, which provides an indication of the quality of the aircraft harness being tested.
The inventor has recognized that there exists, however, a significant problem in maintaining reference quality termini end faces to make accurate measurements. Further recognized by the inventor is that users implementing such fiber-optic harness testing programs have had substantial difficulty in maintaining just two probe end face for the single channel method, and, if employing fiber optic harness testers, such as that manufactured by DIT-MCO, must maintain over 200 end faces clean and free of scratches and pits in order to maintain a reference quality and to prevent the potential of transferring damage from the test side end face to the aircraft fiber end face, or vice versa.
Although the multichannel tester has a potential for saving time, in practice, instead of saving time over the single channel method, more time is needed repeating measurements because the end face was dirty or time is wasted replacing good aircraft fibers rejected and removed because the test side end face was bad (i.e., the unit provides false failures), or a shattered test side end face damages an aircraft fiber end face. Further, such multichannel testing system requires at least two people to manage all the optical test cables and a very large central testing unit. Additionally, the optical cables of the mating harness which optically interface the central testing unit with the aircraft harness, and the connectors for the mating harness which house the fiber optic termini are extremely susceptible to breakage. In practice, such fiber-optic cables frequently suffer damage due to other equipment or personnel transiting between the central testing unit and the end connectors that interface with the aircraft harness connectors.
Accordingly, recognized is the need for a fiber-optic testing apparatus capable of testing fiber optic harnesses, which improves the ease, speed, and accuracy of testing fiber-optic harnesses, which is portable and easy to manipulate by a single person, which does not use a mating harness containing optical cables, and which does not require optical fiber-optical fiber contact between fiber optic termini. Also recognized is the need for a method of retrofitting fiber-optic termini for a test lead connector for an analyzer of a fiber optic harness testing apparatus which uses electrical cabling instead of optical cabling in its mating harness.